1. Field of the Invention
The invention relates to a method for operating a Coriolis mass flow measuring device, whereby the Coriolis mass flow measuring device has at least one measuring tube through which a medium flows, at least one oscillation generator, at least one first oscillation sensor, at least one second oscillation sensor, and at least one control and analysis unit, whereby excitation signals can be routed to the oscillation generator from the control and analysis unit via at least one excitation channel, whereby a first primary measuring signal of interest can be routed to the control and analysis unit from the first oscillation sensor via at least one first measuring channel, and a second primary measuring signal of interest can be routed to the control and analysis unit from the second oscillation sensor via at least one second measuring channel. Moreover, the invention also relates to a Coriolis mass flow measuring device, with which the above-mentioned method is executed.
2. Description of Related Art
Coriolis mass flow measuring devices are primarily used in industrial process measuring technology, where mass flows have to be determined with high accuracy. The mode of operation of Coriolis mass flow measuring devices is based on the fact that at least one measuring tube through which a medium flows is excited to oscillate by an oscillation generator, whereby the mass-loaded medium is fed back to the wall of the measuring tube based on the Coriolis inertial force produced by two orthogonal velocities—that of the flow and that of the measuring tube. This feedback of the medium to the measuring tube results in a change in the measuring tube's oscillation in comparison to the oscillation state of the measuring tube without flow. By ascertaining these characteristics of the oscillations of the flow measuring tube—phase difference, and thus, time difference between the deviations of two measuring tube regions, which oscillate in phase in the state of the measuring tube without flow—the mass flow through the measuring tube can be determined with high accuracy. In the case of homogeneous media, accuracies of approximately 0.04% of the measurement value can be achieved with high-grade Coriolis mass flow measuring devices, and thus, Coriolis mass flow measuring devices are also frequently used in legal metrology.
The high accuracy requirements can only be maintained when the state of the Coriolis mass flow measuring device is ascertained exactly and values influencing the measuring results are taken into consideration when calculating the mass flow. To this end, information-carrying signals, i.e., the excitation signals (currents and/or voltages) and the primary measuring signals of interest, i.e., the deviations of the measuring tube, are ascertained via measuring channels. Also, other known influencing variables, such as, e.g., temperatures and mechanical voltages at significant points of the measuring tube, can be ascertained via measuring channels and are taken as a basis for determining the mass flow by use of the Coriolis mass flow measuring devices. Such methods are frequently based on a mathematical model of the Coriolis mass flow measuring device, whose internal model parameters are determined during the measuring operation, in such a way that a correction to the mass flow measurement is possible in continuous operation (see, e.g., Schröder, T., Kolahi, K., Röck, H.: “Neuartige Regelung eines Coriolis-Massedurchflussmessers [Novel Adjustment of a Coriolis Mass Flow Measuring Device],” Technisches Messen [Industrial Measurement] 71, 2004, pages 259-268).
Coriolis mass flow measuring devices are suitable not only for determining mass flow, but they can also be used, for example, for determining the fluid density and the viscosity of the medium. Specifically, they are also suitable for ascertaining diagnostic parameters, such as, for example, the ascertaining of a multi-phase flow or the ascertaining of deposits. Also, with respect to these variables, there is strong interest in, as precise as possible, ascertaining of measurement values and primarily continuously precise ascertaining of measurement values. The desire for an ensured precise measurement is motivated particularly also by considerations with respect to safety, for example, to achieve specific safety requirement stages—Safety-Integrity Level (SIL).